Abstract:
Sustainable operation of battery powered wireless embedded
systems (such as sensor nodes) is a key challenge, and considerable
research effort has been devoted to energy optimization of such systems.
Environmental energy harvesting, in particular solar based, has emerged
as a viable technique to supplement battery supplies. However, designing
an efficient solar harvesting system to realize the potential benefits of
energy harvesting requires an in-depth understanding of several factors.
For example, solar energy supply is highly time varying and may not
always be sufficient to power the embedded system. Harvesting components,
such as solar panels, and energy storage elements, such as batteries
or ultracapacitors, have different voltage-current characteristics, which
must be matched to each other as well as the energy requirements
of the system to maximize harvesting efficiency. Further, battery nonidealities,
such as self-discharge and round trip efficiency, directly affect
energy usage and storage decisions. The ability of the system to modulate
its power consumption by selectively deactivating its sub-components
also impacts the overall power management architecture. This paper
describes key issues and tradeoffs which arise in the design of solar
energy harvesting, wireless embedded systems and presents the design,
implementation, and performance evaluation of Heliomote, our prototype
that addresses several of these issues. Experimental results demonstrate
that Heliomote, which behaves as a plug-in to the Berkeley/Crossbow
motes and autonomously manages energy harvesting and storage, enables
near-perpetual, harvesting aware operation of the sensor node.